Launch pit complete, ready for Bertha

Last spring, a field of unturned dirt marked the spot where Bertha will begin digging the two-mile State Route 99 tunnel beneath downtown Seattle. One year and 86,000 cubic yards of soil later, it’s a pit fit for the world’s largest tunneling machine.

Crews finished building Bertha’s 80-foot-deep launch pit on Sunday after nearly a year spent building its underground walls, removing soil and building the infrastructure needed to support the nearly 7,000-ton machine. Its completion clears the way for tunneling to start this summer, once Bertha’s 41 pieces have been reassembled and tested at the bottom of the pit.

“If Bertha is the star of the project, the launch pit is her stage,” said Linea Laird, Washington State Department of Transportation administrator for the Alaskan Way Viaduct Replacement Program. “Completing the launch pit means we’re that much closer to the start of tunneling.”

Launch-pit construction started last summer in the work zone west of Seattle’s stadiums. Before excavation began, crews drilled more than 200 piles as many as 100 feet into the ground to form the pit’s walls. The perimeter of the pit is 80 feet wide and 400 feet long.

Assembly of the machine started at the south end of the pit shortly after it arrived last month from Osaka, Japan. Now that the front end of the pit is complete, crews have started building the body of the machine near the spot where it will first push into Seattle’s soil.